This invention relates to a brake unit for an elevator hoist apparatus.
FIGS. 1 and 2 show a conventional elevator hoist apparatus and more particularly a brake unit therefor. In the figures, reference numeral 1 indicates a passenger car of an elevator, 2 indicates a hoist rope supporting the elevator car 1, and 3 indicates a drive pulley around which the hoist rope 2 is wound for driving the hoist rope 2 upwardly and downwardly. The drive pulley 3 is driven by a drive source such as an electric motor 4 through an unillustrated gear unit. Reference numeral 5 is a guide pulley for positioning a counterweight 6.
Also, 7 indicates a brake unit mounted on a drive shaft 8 between the motor 4 and the gear unit. The brake unit 7 usually prevents the rotation of the drive shaft 8 except when the elevator car is travelling. 9 indicates a fixed structure such as a building which supports the gear unit and the drive rope pulley 3.
The brake unit 7 will now be as a brake unit for a hoist apparatus, the brake unit 7 usually is a drum brake, structure of which is generally as illustrated in FIGS. 1 and 2 and 4.
In the figures, reference numeral 10 indicates a brake drum secured to the drive shaft 8, about which brake shoes 11 capable of engaging and separating with respect to an outer circumference thereof are attached to brake arms 13 rotatable about a pivot 12. The brake arms 13 are biased at the side remote from the pivot 12 by springs 14 which cause the brake arms 13 to be urged toward each other or, more particularly, cause the brake shoes 11 attached to the brake arms 13 to be pressed against the outer circumferential surface of the brake drum 10. Also provided on the side of the brake arm remote from the pivot 12 is an electromagnet 15 for opening the brake arms 13 against the biasing force of the springs 14.
Since the conventional brake unit 7 is constructed as described above, the brake drum 10 is not usually rotatable because of the spring braking force of the spring 14 applied through the brake arms 13 and the brake shoes 11, so that the elevator car 1 cannot move up and down. Also, when it is desired to drive the elevator car 1 up and down, the electromagnet 15 is energized, whereby the operating lever of the electromagnet 15 causes the brake arms 13 to rotate open about the pivots 12 against the spring force of the springs 14, so that the brake shoes 11 are separated from the brake drum 10 to release the brake and allow free rotation of the drive shaft 8, so that the elevator car 1 can be driven up and down by the motor 4.
Since the brake unit for an elevator hoist apparatus is constructed and operated as described above, the brake drum 10 is mounted to the drive shaft 8 of the motor 4 and has a long length because its outer circumferential surface is used as the braking surface, so that the axial length of the gear box 16 containing the motor 4, the brake apparatus 7 and the gear unit is large. This may cause a clearance defined between the gear box and the wall surface of the building 9 to become too narrow to achieve a reasonably easy maintenance. Also, since the springs 14 project perpendicularly relative to the axis of the drive shaft 8, the distance to the wall surface of the building 9 is small, so that the installation and maintenance of the springs 14 are difficult, and also the brake shoes 11 must be made large because of the limitation imposed on the brake surface, and the brake arms must disadvantageously be made correspondingly large.